This invention relates to steel rule die cutting and more particularly to an improved multi-cavity die with movable and adjustable cutting units which can be easily and precisely spaced relative to each other and which provide even and consistent cuts.
Steel rule dies are commonly used for cutting cloth and cloth-like substances such as natural textiles and synthetic materials like vinyl. Steel rule dies are particularly advantageous in the repetitive cutting of a specific shape for use in clothing, furniture, shoes, and automotive trim panels. In brief, a steel rule cutting die typically comprises a base substrate or backing board in which grooves are cut and lengths of sharpened blade, known as steel rule, are formed to the same shape as the grooves and inserted in the grooves. The grooves are cut in the substrate in the pattern that is desired to be cut out of the material. Thus, when the steel rules are placed into the grooves, they form cutting edges in the shape of the desired patterns. These dies are used together with a cutting press that forces them against and into a stack of material in order to cut the material. Multiple layers of material can be cut with one pressing operation. Typically, one die will include several cutting unit cavities, each with a different pattern and defined by a closed length of rule, so that several multiple patterns can be cut during a single pass through the press. Multiple cavities on a single die are nested together in an efficient configuration to minimize scrap material.
One problem with typical steel rule dies is that, once the groove is cut into the substrate and the steel rule is placed into the groove, the cavities are permanently arranged in the die. If the pattern of one cavity needs to be modified in any respect, it is necessary to construct a completely new die at significant expense. In other words, there is no flexibility to change the patterns without performing the costly and time consuming procedure of making a whole new die. Additionally, the forces created on such a steel rule during cutting are concentrated on the narrow surface area of the rule that contacts the substrate. As a result, the steel rule is driven into the substrate during cutting operations until it can no longer perform a cutting function. Moreover, the rule can be torqued and damaged when the forces are unevenly distributed along the steel rule and only a portion of the rule is driven into the substrate.
A previous attempt at solving these problems is described in U.S. patent application Ser. No. 08/949,855, now U.S. Pat. No. 5,983,766, entitled “Steel Rule Die with Removable Cutting Units and Method for Using Same” which is herein incorporated by reference. The application discloses a die which provides flexibility in die cutting patterns by making the cavities part of different cutting units that are separate from, and removably attached to, a substrate. Removal of the cutting units from the primary substrate allows cleaning of scrap material and allows the shape of the cavities to be modified. However, when the cutting units are positioned on the substrate, the spacing between steel rules of the adjacent cutting units is not controlled, and in some instances, the steel rules of adjacent cutting units may be touching each other. Under this arrangement there is a possibility that scrap material can become lodged between and deform the adjacent lengths of the steel rules.
Large cutting dies used particularly in the automotive industry contain a primary substrate made of high grade plywood. The reasons for using plywood include that it is readily available, relatively inexpensive, light weight and easily maneuvered. However, as discussed above, positioning a steel rule with a very small surface area directly on a softer wooden substrate can result in problems, such as the steel rule diving into the wooden substrate under the loads created during cutting. As a result, the height of the steel rule will decrease and eventually the die will stop cutting. This requires that the cavities be moved to another place on the substrate, thereby resulting in significant maintenance costs. In addition, when a steel rules dives unevenly into the wood, the rule will tend to bend over sideways and become damaged. Attempts have been made to add a hard coating to the plywood substrate to prevent the rule from diving into it. While this helps, it does not solve the problem.
Attempts have been made to mount movable cavities with cross braces on top of wooden primary substrates. One such attempt is disclosed in WO 98/09781 to Geffros et al. The disclosed cutting knife assembly includes a plurality of cutting units with elongated strips serving as cross braces. Each cutting unit has a cutting rule and a plurality of cross members which include mounting holes for securing the cutting unit to the substrate. However, these cross members do not extend under the rule to prevent it from diving into the wooden substrate, nor do they distribute the forces applied to the rules during the cutting process over a widened surface area that is as large or larger than a cavity bounded by the steel rule. Instead, the forces remain highly concentrated along the lengths of the rule with some of the forces being transferred to the spaced cross members. Moreover, the portions of the rule that do not dive into the substrate can cause the rule to torque and deform. The elongated shape of the cross member makes the cross braced cutting units susceptible to deformation during the mounting and subsequent cutting operations, thereby effecting the quality of the final product. Consequently, the expensive and time consuming task of disassembling the die and replacing the substrate will need to be performed on a frequent basis.
Another problem with the current dies using replaceable cavities is internal cutouts. Material is ejected out of the top of the tool rather than through the back of the tool, requiring frequent cleaning of scrap material from the cutting die. In addition the solid cutouts are not themselves movable with respect to the outer perimeter of the cavity, thereby making adjustments and changes difficult.